Rebuilt l28 only runs with fuel pump unplugged

[jhill]

Hello all.

A few specifics first.

I just got finished rebuilding my n42 head n42 block with schnieder 270-80f cam. Stock bosch e.f.i., stock injectors, pallnet fuel rail, 6-1 header, head shaved, kameari adjustable cam pulley.

Now the issue is I am trying to get it to start (it ran on all of this before engine rebuild) and it will only start with the fuel pump unplugged and when the fuel pressure gauge hits 0.

I want to properly break in the cam so I only let it run for a second or 2 and as soon as I plugged the pump back in it died.

My thought is time get an adjustable fuel pressure regulator, or maybe swap the old fuel rail back in which I don't want to do.

Please any similar situations, or ideas would be greatly appreciated.

[NewZed]

  it will only start with the fuel pump unplugged and when the fuel pressure gauge hits 0.

My thought is time get an adjustable fuel pressure regulator, or maybe swap the old fuel rail back in which I don't want to do.

 

So that you can adjust the pressure to zero?  Where does the pressure start and where is the gauge located in the system?

 

Is it pump unplugged AND zero pressure.  Or is it one or the other.  Coincidence.  And,  as soon as I plugged the pump back in it died, OR is it as soon as pressure increased it died.  One could be electrical and one could be fuel pressure.

 

Kind of sounds like your injectors are shorted and wide open, flooding the engine.  You can check that with a meter.  Key On they should measure the same on each terminal of the plug (measure from the back of the plug with the injector still connected to the injector), about battery voltage.  If they're shorted one side will measure lower voltage.

[luseboy]

How is the fuel pump wired in? Sounds like there's likely a problem with the fuel pump shorting another circuit out or perhaps some sort of safety measure that it trips when it's running. Intersting problem for sure.

[supernova_6969]

a few things could be done to test out the various potential issues...

 

-first I'd check what pressure is in the fuel rail;  maybe your regulator is dead that you're super rich... also, maybe your return line is clogged, which would do the same thing.  

-second, i'd check to see if the injectors are working, as NewZed suggested..   you probably know about putting a screwdriver on them and listening for the clicks.. if you're particularly daring, you can leave the injectors wired and on the rail, but disconnect the lot from the engine, then put a container under each injector and have an assistant turn the key this way.  you'll see if your injectors are pulsing properly.  it's a little cow-boy, but can't beat the data from it. 

-third, basked on luseboy, i'd unplug the pump, and run a wire straight from the battery (with a big fat fuse) to the pump, and try to run the engine that way.  if the pump wiring shorts something out, that'll stop the short and have your fuel pump working.

[jhill]

Newzed hit the nail on the head. Injectors were stuck open. Took a little head scratching and plenty of wtf's but after changing the dropping resistors out for another set and the ignition transistor (not sure if that's the actual name) and cleaning all wiring harness grounds the problem is fixed.

 

Now, after I ran the car, I wiped out the new schneider cam....so back went in the old stock cam, only to find the rockers hit the top of the valve springs. Is there supposed to be a shim under the valve springs or did my machine shop add these without me knowing?

Edited April 27, 2016 by jhill

[Xnke]

Need photos of the valve train.

 

Also, if you wiped a cam, the rocker arms are toast. Also your engine is now full of extremely abrasive cast iron powder.

 

Wiping a cam lobe sucks.

Edited April 27, 2016 by Xnke

[jhill]

I'll take photos today. I had purchased new rockers for the new cam and kept the old rockers in order in case I needed to go back to the old cam. They are in good shape and will be back on the lobes they came from.